186 BIOLOGICAL ASPECTS OF HUMAN PROBLEMS 



adult cells. This is true, at least, in the case of 

 some of the tissues. 



Thus the developed human body consists of 

 myriads of cells that have lost, in a greater or less 

 degree, their powers of reproduction (though this is 

 partially maintained by some kinds of cells) . There 

 is nothing to indicate that this power of reproduc- 

 tion can be restored to them. This means that, 

 after a time, death is inevitable. In each sex, how- 

 ever, a relatively small number of cells have been 

 set aside that, by some wholly inscrutable mechanism, 

 are laden with hereditary qualities or memories. 

 The individual germ cells (at least in the case of the 

 female), like the somatic cells derived from the 

 parent germ cells, have undergone some develop- 

 ment. But this slight development, be it noted, 

 has not been attended by an expenditure of the 

 powers of reproduction. These cells, therefore, still 

 possess their specific reproductive powers, though 

 these lie latent unless impregnation occurs. The 

 germ cells of both sexes hold stores of energy that 

 may be likened roughly to the potential forces exerted 

 by rivers that have been dammed back. It is the 

 destiny of the incomparably greater number of the 

 germ cells never to have their stored energy released 

 in reproduction. Yet for a relatively few female 

 germ cells the restraining barriers are torn away by 

 the energy contributed to them by the heads of the 

 male germ cells or spermatozoa. The junction of 

 the male cell with the female cell is like the acces- 



